The sordid story surrounding the resignation of CIA Director David Petraeus continues to grow. This morning there's word that the top U.S. commander in Afghanistan, Gen. John Allen, is under investigation for "inappropriate communications" with the woman who kicked off the chain of events that led to the uncovering of the extramarital affair Petraeus was having (with a different woman) and his resignation.

Allen, as NPR's Tom Bowman reported on Morning Edition, has told Pentagon officials that he did nothing wrong. But investigators have discovered, officials say, 20,000 to 30,000 pages of emails and electronic documents sent between Allen and Jill Kelley, 37, of Tampa. The Pentagon is now investigating Allen's communications with Kelley. Allen's nomination to be commander of U.S. and NATO forces in Europe has been put on hold.

With Allen's entrance into the story and the new twist involving Kelley, this seems like a good time for a guide to who's who and what's what:

-- Retired Gen. David Petraeus. The former top U.S. commander in Afghanistan, the 60-year-old Petraeus became director of the CIA in the summer of 2011. It was sometime after he left the Army and took over at the CIA, Petraeus has reportedly told friends, that he began an affair with Paula Broadwell. She's a now-40-year-old major in the Army Reserve. They reportedly ended the affair about four months ago. This morning's Washington Post reports that some of the retired general's advisers say he "planned to stay in the job even after he acknowledged the affair to the FBI, hoping the episode would never become public. He resigned last week after being told to do so by Director of National Intelligence James R. Clapper Jr. on the day President Obama was reelected."

-- Paula Broadwell. A specialist in counterterrorism issues as well as an Army reservist, Broadwell is the author of All In: The Education of General David Petraeus, a biography of Petraeus. While working on that book, she lived and worked with the then-general's staff in Afghanistan. Like Petraeus, she is married. On Monday, FBI agents were seen searching her home in Charlotte, N.C.

-- Jill Kelley. Described in reports as a volunteer social liaison with military families at MacDill Air Force Base in Tampa, Kelley knows Petraeus and his wife Holly. Earlier this year, she reportedly told an acquaintance who works for the FBI about harassing emails she had been receiving. During that investigation, the FBI traced the emails to Broadwell. According to The New York Times, officials say Broadwell "saw Ms. Kelley as a rival for her affections with Mr. Petraeus." As the FBI investigated the emails to Kelley, agents turned up online messages exchanged by Petraeus and Broadwell that revealed their affair. Kelley is married.

43. Perhaps Gen. Allen is workng for Wikileaks.

47. print an email and see how many pages it is.

if you include header info, as well as the previous original email messages contained in a response, one short email could be many pages long. probably just a few thousand emails that are several pages long.

7. Why would some no-name rate a ghostwriter?

I thought those were for big named people who didn't have writing experience but wanted to collaborate on an auto-biography or tell-all? How does somebody who just wants to write a biography of a famous person rate a ghostwriter who is the editor of a big name paper? Shouldn't he have just done the interviews and written the book himself? What was she needed for, besides the obvious at this point?

14. Good question

Even unknown people with ideas for a story hire ghostwriters now -- because they want to see their name on the cover of a book -- but it's getting ridiculous.

If Broadwell paid that Vernon guy, he no doubt did it strictly for the money, not thinking it would become a bestseller (I hope royalties are part of his agreement!!!). But if the publisher optioned it before it was even written, why would THEY pay for (or merely approve) a ghostwriter when Paula Broadwell isn't famous and doesn't have a platform?

It's the least important aspect of the story, but I'm curious how the book itself came to be.

The whole thing is just weird. Can't wrap my brain around it all yet...lol

25. It could be more important than it seems

Who connected her with Petreaus to do this book then connected her to a Washington Post editor to be her ghostwriter? It just doesn't seem like she was someone who would get all these important connections since she hadn't written a book before. Is there someone who connects these dots?

Loeb did not respond to a request from The Huffington Post on working with Broadwell, but spoke favorably in January about his co-author's reporting skills and how the two teamed up on a biography that grew out of her Harvard University dissertation.

In June 2010, when President Barack Obama tapped him to take charge in Afghanistan for what would become Petraeus' final command, Broadwell knew the time was right to parlay her dissertation into a biography.

Soon, she had an agent and a contract from Penguin Press. To help organize and write the book, she teamed with The Washington Post's Vernon Loeb. Broadwell proved to be an "absolutely intrepid" reporter, Loeb says, dictating from airports, filling up his email inbox and delivering "this fire hose of information."

Loeb suspects the media's interest in their book stems at least a bit from Broadwell herself. It's audacious, he says, "that she even attempted this. Here she has two young kids, a husband who's a doctor, and yet ... she's writing a book of this magnitude and hardly breaking a sweat."

17. the whole ghostwriting thing

As a professional ghostwriter, I have to laugh at your comment. If people only knew how few books are actually written by their famous "authors," they'd laugh, too. And if I could find a way to clone myself into quintuplets, my trips to the bank would be nearly hysterical. But just so you know, it sometimes takes holding your nose. I've written books on subjects so boring to me personally that I felt like a prisoner of war. I've also written a few that oppose my personal idealogies. But it's a living.

38. with good cause. See how many marriages just went on the rocks here?

18. It starts to sound like the entire upper echelon is one big Boink Festival.

The President can't even make his way into the War Room without having to step over copulating couples in the halls.

The only thing saving the republic is that Mitch McConnell keeps showing up at republican caucuses wearing nothing but a sequined jockstrap and carrying a bottle of Mazola. That usually turns off enough people to enable them to focus on important business -- like getting re-elected -- long enough to keep up appearances.

22. Who is General John R. Allen?

In June 2008 Secretary of Defense Robert Gates announced Allen's nomination for promotion to the rank of lieutenant general. He served as the deputy commander of the U.S. Central Command from 15 July 2008 – 1 June 2011 at MacDill Air Force Base. On June 30, 2010 Allen temporarily commanded Central Command after General David Petraeus left to assume command of the International Security Assistance Force in Afghanistan. He served as acting commander until General James Mattis took command on August 11. Allen was promoted to general by Chairman of the Joint Chiefs of Staff, Admiral Mike Mullen prior to his assumption of command of ISAF, and U.S. Forces Afghanistan (USFOR-A) on 18 July 2011

39. Well, we don't know all the favors he did for her yet..

A mistress is a long-term female lover and companion who is not married to her partner; the term is used especially when her partner is married. The relationship generally is stable and at least semi-permanent; however, the couple does not live together openly. Also the relationship is usually, but not always, secret. There is an implication that a mistress may be "kept"—i.e., that the lover is paying for some of the woman's living expenses.